Defocusing device for optical systems

ABSTRACT

To produce a totally blurred image in the dissolution of a moving-picture scene, a camera objective of the varifocal type is provided with an iris diaphragm whose leaves consist of lightscattering translucent material.

United States Patent 11 1 1111 3,784,290 Strobel et al. Jan. '8, 1974DEFOCUSING DEVICE FOR OPTICAL [5 6] References Cited SYSTEMS v UNITEDSTATES PATENTS [75] Inventors: Joseph StrObeLRoxheim; Norbert 745,31312/1903 Bate 95/64 Beisiegel, Traisen, both of Germany 1,530,238 3 1925Corlett.... 95/64 v 3,603,676 9/1971 Loewe [73] Ass1gnee: Jos. Schneider& C0-, op 2,148,508 2/1939 Seitz 352/91 I Werke, Bad Kreuznach, Germany[22] Filed: May 24, 1972 Primary Examiner-John M. Horan At 1 F. R t l.[21 Appl. No.: 256,246 Omey Kat a [57] ABSTRACT [30] Foreign ApphcatmnPnomy Data To produce a totally blurred image in the dissolution May 26,1971 Germany..- P 2l 26 131.4 of a moving picture Scene, a cameraobjective of the varifocal type is provided with an iris diaphragm [52]U.S. Cl. 352/91 whose leaves consist of light scattering translucent[51] Int. Cl. G03b 21/36 material 1 [58] Field of Search 352/91 Y 5Claims, 4 Drawing Figures A A Jfi 4 3 Blurring Diaphragm 2 FocusingDiaphragm PATENTED JAN 81974 4 Trans/ucenr P/astic 4 3 BlurringDiaphragm SOLAR '21 CEtL D/A PHRAGM CONTROL 1 DEFOCUSING DEVICE FOROPTICAL SYSTEMS Our present invention relates to the technique ofdefocusing a photographically projected image for the purpose ofcreating an effect of dissolution of a moving-picture scene, either inthe filming of motion pictures or on television.

Such dissolution effects can be conventionally realized by the shiftingof one or more objective lenses. With this procedure, however, onegenerally causes only a partial blurring .of the image while other partsthereof may even be brought into sharper focus. Moreover, systems fordefocusing an objective in this manner are rather complex andinconvenient to operate.

It is known, e.g., from US. Pat. No. 3,603,676, to create such ablurring effect by inserting a diaphanous light-dispersing plate betweentwo lenses of an objective, the plate being introduced from the side soas to cause an unsymmetrical cutoff of a progressively increasing numberof light rays passing between these lenses. A uniform dimming of thepicture (or, conversely, a brightening thereof upon the withdrawal ofthe light-scattering plate) is possible with such an arrangement only ifthe plate motion occurs in close proximity to the plane of a focusingdiaphragm acting as an aperture stop.

The general object of our present invention is to provide an opticalsystem affording greater flexibility in the positioning of the movabledefocusing element.

A more particular object" is to provide a defocusing element which canbe mounted in an objective housing without taking up significantadditional space and without requiring the provision ofa lateral slotfor its operative insertion and withdrawal.

These objects are realized, pursuant to our present invention, byconstructing the defocusing element as a blurring diaphragm centered onthe objective axis, this blurring diaphragm including at least one pairof iris leaves of light-scattering translucent material which aresymmetrically movable toward and away from that axis in the manner ofthe leaves of conventional iris diaphragms.

Such a conventional diaphragm, operable for focusing purposesindependently of the blurring diaphragm, may in fact be alignedtherewith in the space between a front and a rear lens or lens group,yet the two diaphragms may be separated by one or more lenses inasmuchas the fade-in or fade-out effect of the blurring diaphragm will besymmetrical even if that diaphragm is substantially offset from theplane of the exit pupil.

The leaves of a blurring diaphragm according to our inventionadvantageously consist of a synthetic resin, such as polypropylene,which at the thicknesses here considered (fractions of a millimeter) issufficiently light-transmissive even in those regions where adjoiningleaves overlap. It is advantageous, however, to choose the shape of theleaves in such a way as to minimize the extent of their overlap.

The invention will be described in greater detail hereinafter withreference to the accompanying drawing in which:

FIG. 1 is a diagrammatic view of an objective system embodying theinvention: 2

FIG. 2 is a cross-sectional view of a blurring diaphragm forming part ofthe system of FIG. 1;

FIG. 3 is a face view of the blurring diaphragm shown in FIG. 2; and

FIG. 4 is a view similar to FIG. 1, illustrating amodification. 1

The optical system 1 shown in FIG. 1 comprises a varifocal front group Aand a fixed rear group or basic objective B. Front group A consists, ina manner well known per se, of a stationary front lens 11 of positiverefractivity, two axially movable inten'nediate lenses 12 and 13 ofnegative refractivity and a fixed positive rear lens 14. Objective B iscomposed of three air-spaced lenses, i.e., a first lens 15 of weak(preferably positive) refractivity, a biconcave second lens 16 and abiconvex third lens 17. A conventional focusing diaphragm 2, e.g., ofthe iris type, is inserted between lenses 14 and 15 to operate as anexit pupil for the front group A and an entrance pupil for the reargroup B.

In accordance with this invention, a blurring diaphragm 3 is interposedbetween lenses l5 and 16. As more fully illustrated in FIGS. 2 and 3,diaphragm 3 comprises a fixed mounting ring 7, a coaxial control ring 8and a circular array of pivotally mounted iris leaves 4 with pins 5 and6 secured to these leaves, pins 5 being received in holes 5 of ring'7whereas pins 6 are movable in slots 6 of ring 8. Rotation may beimparted to the control ring 8 by a conventional transmission linking itwith a setting ring outside the objective housing. The iris leaves 4 ofdiaphragm 3, the contour of one of which has been indicated in dottedlines in FIG. 3, consist of translucent plastic material and limitedlyoverlap one another when ring 8 is rotated in a sense narrowing thecentral aperture defined thereby. The overall brightness of the imageis, however, only slightly affected by the position of this diaphragm,which is desirable in that it avoids eye strain in the observer.

The low refractive power of lens 15 insures that the blurring diaphragm3, although physically separated from focusing diaphragm 2 by aconsiderable distance, is still sufficiently remote from the focal planeof the objective B to avoid any undesirable vignetting effect.

The relative position of diaphragms 2 and 3 may also be inverted, asshown in FIG. 4. This latter arrangement is particularly advantageouswhere, as likewise illustrated in this Figure, the focusing diaphragm 2is conventionally controlled by a photometer such as a solar cell 18 towhich light rays are directed by a semireflector 19 forming part of aview-finding system with a mirror 20 and an eyepiece 21. The cell 18adjusts the diaphragm 2 through the intermediary of a controller 22which normally is set only in accordance with the brightness of theincident light from front group A (FIG. 1); when the blurring diaphragm3 is actuated, the reduction in light intensity detected by sensor 18,22 is translated into a wider opening of diaphragm 2 so that thebrightness of the image remains substantially constant.

We claim:

I. In a camera objective having rear lens means and front lens meansspaced apart along an optical axis, the combination therewith of ablurring diaphragm with a mounting ring centered on said axis andinterposed between said front and rear leans means, said blurringdiaphragm having a circular array'of iris leaves of lightscatteringtranslucent material pivotally mounted on said ring and symmetricallymovable toward said axis for defocusing an image projected by said frontand rear leans means; an iris diaphragm with opaque leaves aligned withsaid blurring diaphragm and disposed between said front and rear lensmeans beyond said blurring diaphragm as seen in the direction ofincident light; sensing means responsive to the light intensity betweensaid diaphragms; and control means for said iris diaphragm responsive tosaid sensing means for opening said iris diaphragm upon closure of saidblurring dialigned with said blurring diaphragm and disposed betweensaid front and rear lens means beyond said blurring diaphragm as seen inthe direction of incident light; sensing means responsive to the lightintensity between said diaphragms; and control means for said irisdiaphragm responsive to said sensing means for opening said hisdiaphragm upon closure of said blurring diaphragm.

3. The combination defined in claim 2 wherein said translucent materialis synthetic-resin foil.

4. The combination defined in claim 2, further comprising an additionallens interposed between said diaphragms. v

5. The combination defined in claim 4 wherein said additional lens hasnear-zero refractive power.

1. In a camera objective having rear lens means and front lens meansspaced apart along an optical axis, the combination therewith of ablurring diaphragm with a mounting ring centered on said axis andinterposed between said front and rear leans means, said blurringdiaphragm having a circular array of iris leaves of light-scatteringtranslucent material pivotally mounted on said ring and symmetricallymovable toward said axis for defocusing an image projected by said frontand rear leans means; an iris diaphragm with opaque leaves aligned withsaid blurring diaphragm and disposed between said front and rear lensmeans beyond said blurring diaphragm as seen in the direction ofincident light; sensing means responsive to the light intensity betweensaid diaphragms; and control means for said iris diaphragm responsive tosaid sensing means for opening said iris diaphragm upon closure of saidblurring diaphragm.
 2. In a camera objective having rear lens means andfront lens means spaced apart along an optical axis, the combinationtherewith of a blurring diaphragm centered on said axis and interposedbetween said front and rear lens means, said blurring diaphragm havingat least one pair of iris leaves of light-scattering translucentmaterial symmetrically movable toward said axis for defocusing an imageprojected by said front and rear lens means; an iris diaphragm withopaque leaves aligned with said blurring diaphragm and disposed betweensaid front and rear lens means beyond said blurring diaphragm as seen inthe direction of incident light; sensing means responsive to the lightintensity between said diaphragms; and control means for said irisdiaphragm responsive to said sensing means for opening said irisdiaphragm upon closure of said blurring diaphragm.
 3. The combinationdefined in claim 2 wherein said translucent material is synthetic-resinfoil.
 4. The combination defined in claim 2, further comprising anadditional lens interposed between said diaphragms.
 5. The combinationdefined in claim 4 wherein said additional lens has near-zero refractivepower.